Solutions and methods for radioactive decontamination



This invention relates to solutions and methods for radioactivedecontamination.

Radioactive contaminants occur as unstable forms of the elements whichin practical situations may be found in pure form but are usually foundmixed in any of a wide variety of soils. Effective decontaminationinvolves both stabilization and physical removal of the radioactivecontaminant. An object of the invention is to provide improved solutionsand methods for achieving this result.

Previous decontamination methods have been based on an attempt to removethe soil from articles to be cleaned in the hope that its radioactiveingredients would be removed in the process. The process is practiced inthe specific form required for the removal of the soil. On the otherhand, this invention provides a decontamination solution capable ofdirect action on the radioactive contaminant although in practice itwill remove most of the soils as well.

Another object is to provide highly effective solutions fordecontamination when the radioactive contaminant is specificallyidentified; but the provision of solutions which are very effectiveevenvwhen the radioactive contaminant is not known, is also an object.

Another object of the invention is to provide a solution, for generalapplication to the problem of decontamination, sufiiciently effective towarrant its use for average cases, for those cases in which a variety ofradioactive substances are present, and for first decontamination inpreparation for specific contamination in special cases.

Another important object is to provide a solution which is suflicientlyinexpensive to make practical the decontamination of inexpensive handtools such as pliers, screwdrivers, and the like which now must bedisposed of, often after only a single usage.

These andother objects and advantages of the invention which willhereinafter be apparent, are realized by the provision of a radioactivecontaminant comprising a mixture of a detergent liquid, an ion exchangeagent soluble in said liquid to form ions charged oppositely of theradioactive contaminant, and adsorbent solids distributed in the liquid.Each of these ingredients has a specific individual function in thedecontamination process, the effectiveness of each of which depends uponthe function of the other whereby the invention contemplates solutionssimultaneously containing all of these substances. The article to bedecontaminated is immersed in the solution which advantageously issubjected to forces producing cavitation. 1

In addition to their functional interdependence there is a mechanicalcooperation between the substances. The detergent serves as the vehicleby which the exchange agent and adsorbent may move into association withone another and the surface to be cleaned, while the forces exerted bythe substances accounts for that movement. Provision for cavitationaction aids the movement and intermixing of the constituents of thesolvent in addition to providing mechanical force for dislodgingcontaminants and soil from the article being cleaned and from oneanother.

The individual functions of the detergent, ion exchange agent, andadsorbent, taken one at a time, are the functions associated with thosenames by chemists although the action by which the function is providedmay not yet have been defined. The detergent, through the applicaa3,047,434 C3 Patented July e1, 1962 2 tion of hydrophilic, hydrophobic,lipophilic, or lipophobic forces or chelating action, overcomes themechanical forces and affinities which bind the soil and contaminants tothe articlebeing cleaned.

The ion exchange agent, having polarity opposed to the polarity of thecharge associated with the instability or radioactivity of thecontaminant, has an afinity for the contaminant and joins it to form adiscreet particle. The integrity of the union of the exchange agent andcontaminant is preserved by their adherence in combination to theadherent which in turn is prevented by the detergent from adherence tothe article being cleaned.

When the contaminant is identified, the ion exchange agent is selectedin accordance with principles well known in the chemical art so thatchemists having at least ordinary skill can select a proper agent. Whenthe contaminants or some of them are not identified, sulfides,carbonates, hydroxides and sulfates can be utilized. The sodium salts ofthese radicals are preferred in accordance with the invention and apositive ion from this group should be included if there exists apossibility that one of the contaminants is negative.

To augment the action of the exchange agent, the detergentadvantageously includes a chelating agent. In the interest of costreduction as well as for its eflectiveness as a wetting agent inconnection with most soils, it is preferred that the detergent consistprimarily of water. Advantageously the detergent may comprise a mixtureof water and ethylene diam-inc tetra acetic acid.

A wide variety of adsorbents have been used with good results includingsilicates such as a colloidal cl-ay, talc, and fullers earth, chalk;sulfides of arsenic and antimony; diatomaceous earth; carbon black; andmetallic oxides such as alumina, magnesia, iron oxide, and titanium andmanganese dioxide.

Of course, the action of solutions made according to the invention maybe augmented and hastened by mechanical agitation to insure that freshsolution reaches the surface to be decontaminated and by mechanicalactions on the soil itself.

A superior kind of such mechanical action is ultrasonic cavitation ofthe decontamination solution and the solution found to be mostadvantageous for general decontamination is entirely compatible withthis kind of action. That solution comprises water, ethylene diaminetetra acetic acid, sodium sulfate, sodium hydroxide, manganese dioxide,and carbon black.

By way of example and not of limitation, since other solutions arepossible and the relative quantities in this solution may be modifiedwithin the scope of the invention and the appended claims, aparticularly effective solution for decontamination was made by themixing of ingredients in the following proportions:

milliliters of water, 1 gram ethylene diamine tetra acetic acid, 0.2gram sodium sulfate, 0.2 gram sodium hydroxide, 0.1 gram manganesedioxide and 0.1 gram carbon black. A soiled article having radioactivecontaminants, especially radioactive cesium 134, was immersed in thissolution.

Also, a similarly contaminated article was immersed in a like solutionand the latter was activated to produce cavitation bythe action ofultrasonic energy with improved result.

I claim: I

1. A solution for radioactive decontamination comprising a mixture ofwater, ethylene diamine tetra acetic acid, sodium sulfate, sodiumhydroxide, manganese dioxide, and carbon black.

2. The decontamination method which comprises immersing a radioactivelycontaminated article in a solution comprised of water, ethylene diaminetetra acetic acid, sodium sulfate, sodium hydroxide, manganese dioxide,

3 4 and carbon black, and subjecting said solution to ultra- 2,401,484Jackson June 4, 1946 sonic vibration forces sufiicient to producecavitation 2,607,738 Hardy Aug. 19, 1952 therein. 2,672,449 Snell Mar.16, 1954 2,678,303 Bonewitz May 11, 1954 References Cried 1n the file ofth1s patent 5 2,736,640 McGraW Feb- 28 1956 UNITED STATES PATENTS2,739,882 Ellis Mar. 27, 1956 2,016,265 Doherty Oct. 1, 1935 2,802,758Kearney Aug. 13, 1957 2,241,984 Cooper May 13, 1941 2,814,575 Lange NOV.26, 1957

1. A SOLUTION FOR RADIOACTIVE DECONTAMINATION COMPRISING A MIXTURE OFWATER, ETHYLENE DIAMINE TETRA ACETIC ACID, SODIUM SULFATE, SODIUMHYDROXIDE, MANFANESE DIOXIDE, AND CARBON BLACK.
 2. THE DECONTAMINATIONMETHOD WHICH COMPRISES IMMERSING A RADIOACTIVELY CONTAMINATED ARTICLE INA SOLUTION COMPRISES OF WATER ETHYLENE DIAMINE TETRA ACETIC ACID, SODIUMSULFATE, SODIUM HYDROXIDE MANGNASES DIOXIDE, AND CARBON BLACK ANDSUBJECTING SAID SOLUTION TO ULTRASONIC VIBRATION FORCES SUFFICIENT TOPRODUCE CAVIATION THEREIN.